Best PracticesJoinery Methods for Z-Girt Sub-Framing

December 21, 2020

Joinery methods of z shaped girts can play a major role in the structural integrity of a building. There are several different joinery methods that can be used with advantages and disadvantages to all.

Sub-framing girts are typically manufactured in limited lengths, such as 8′ for example. This is necessary for installation purposes. One person can typically install an 8′ girt alone. This can have an affect on project plans as most wall lengths are more than 8′ in length.

The ends of the girts must then be joined to create continuity along the wall. Some critical engineering metrics that need to be considered for these end conditions are:

  • Structural stress and deformation analysis
  • Attachment detail to substrate
  • Allowance for thermal expansion along the length of the girt


The most common wall configuration includes horizontal installation of z-shaped girts over vertical studs. The girt lateral joinery detail is required for structural calculations for horizontal installation of z-shaped girts over vertical studs. This covers the most common joinery methods for girts.


Lap Joints — Traditional Metal

Traditionally, steel Z girts are made of relatively thin metal (i.e. 0.062”) with a high value of elasticity and stiffness. This allows them to easily lap and stitch together with a lap joint method.

Due to the increased relative thickness of composite or FRP girts compared to steel girts, lap joint methods are not easily possible in FRP z-shaped girts. When attempted with thicker girts, it creates out of plane offsets in the wall’s vertical plane.

Lap Joints - Joinery Methods - Z Girt Sub Framing Joinery Methods Lap Joint Method for Steel Z-Shaped Girt[/caption]


Butt Joints — Standard FRP

Butt joints place each girt end on half of a stud. This joinery method is unacceptable on a single stud for best practice considerations due to a minimum required margin space of 2.5 fastener diameters at the end of girt for FRP (0.25” fastener diameter x 2.5 required margin space + 0.25” fastener + 0.1875” metal edge margin x 2 sides = minimum flange width of 2.125”). To effectively use butt joints with FRP girts, double studs are needed at every FRP girt joint, leading to increased material and labor costs.

Butt Joints - Joinery Methods Butt Joint Method for FRP Z-Shaped Girt[/caption]


Cantilever Joints — Standard FRP

The cantilever joinery method involves installing girts horizontally with a cantilever over the studs on both ends. For structural calculations, the maximum possible cantilever for the worst typical case should be used.

Cantilever Joints - Joinery Methods Cantilever Joint Method for FRP Z-Shaped Girt[/caption]


Interlocking Joints — Composite Metal Hybrid

The GreenGirt composite metal hybrid (CMH) z-shaped girt has an integral interlocking system that enables one end of a girt to connect into the adjacent girt. The patented design of the GreenGirt Simple Z allows for ease of connection and installation of the z-shaped girt while providing best practice structural integrity.

Interlocking Joints - Joinery Methods
Interlocking Joint Method for GreenGirt Simple Z


Importance of Joinery Methods

With different joinery methods possible using varying z-shaped girt materials, it is important to consider real life installation and application of the joint type. If appropriate joinery methods are not used, the structural integrity of the building could be at risk of failure.

SMARTci and GreenGirt provide best practice solutions for buildings with continuous insulation and building rainscreen systems. GreenGirt provides a thermal break and mounting platform for cladding applications creating an insulated building envelope with universal compatibility for any substrate, insulation, or cladding.

Specially designed to eliminate thermal gaps that other systems neglect, the SMARTci continuous insulation (CI) systems leverage the insulated composite metal hybrid (CMH) GreenGirt Simple Z technology for a full rainscreen attachment and CI solution. Superior to steel structurally and thermally, GreenGirt provides the same loading capabilities of a z girt of equivalent depth. Additionally, GreenGirt is not susceptible to moisture, corrosion, or electrochemical reactions.

Click here to learn more about the the Joinery Method of SMARTci GreenGirt systems. Or contact an A2P Representative today to receive a custom quote.

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Comparing Z-Girt Material Quality

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Structural Engineering for Composite Sub-Framing Materials

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